1. Field of the Invention
The present invention relates to mass-transfer trays for chemical process columns and, more particularly, but not by way of limitation, to improved hinge joints in mass transfer trays for higher efficiency and increased capacity operation.
2. History of Related Art
Distillation columns are utilized to separate selected components from a multicomponent stream. Generally, such contact columns utilize either trays, packing, or combinations thereof. In certain years the trend has been to replace so-called “bubble caps” by sieve and valve trays in most tray column designs.
Successful fractionation in the column is dependent upon intimate contact between heavier fluids and lighter fluids. Some contact devices, such as trays, are characterized by relatively high pressure drop and relatively high fluid hold-up. One type of contact apparatus utilizes fluid in the vapor phase to contact fluid in the liquid phase and has become popular for certain applications. Another type of contact apparatus is high-efficiency packing, which is energy efficient because it has low pressure drop and low fluid hold-up. However, these very properties at times make columns equipped with structured packing difficult to operate in a stable, consistent manner. Moreover, many applications simply require the use of trays.
Addressing now select flow designs, a particularly effective tray in process columns is a sieve tray. The sieve tray is constructed with a large number of apertures formed in a bottom surface. The apertures permit the ascending lighter fluid to flow into direct engagement with the heavier fluid that is flowing across the sieve tray from the downcomer described above. When there is sufficient lighter-fluid flow upwardly through the sieve tray, the heavier fluid is prevented from running downwardly through the apertures (referred to as “weeping”). A small degree of weeping is normal in trays while a larger degree of weeping is detrimental to the capacity and efficiency of a tray.
When a vapor comprises the lighter fluid and a liquid comprises the heavier fluid, there are specific performance issues. Certain performance and design issues are seen in the publication “Distillation Tray Fundamentals”, M. J. Lockett, Cambridge University Press, 1986. Other examples are seen in several prior art patents, which include U.S. Pat. No. 3,338,566 issued to W. Kittel, U.S. Pat. No. 3,729,179 assigned to Fractionation Research, Inc., U.S. Pat. No. 4,275,021 assigned to Union Carbide Corporation and U.S. Pat. No. 4,603,022 issued to Mitsubishi Jukogyo Kabushiki Kaisha of Tokyo, Japan. U.S. Pat. No. 4,499,035 assigned to Union Carbide Corporation teaches a gas-liquid contacting tray with improved inlet bubbling means. A cross-flow tray of the type described above is therein shown with improved means for initiating bubble activity at the tray inlet comprising spaced apart, imperforate wall members extending substantially vertically upwardly and transverse to the liquid flow path. The structural configuration is said to promote activity over a larger tray surface than that afforded by simple perforated tray assemblies. This is accomplished in part by providing a raised region adjacent the downcomer area for facilitating gas ascension therethrough.
U.S. Pat. No. 4,550,000 assigned to Shell Oil Company teaches an apparatus for contacting a liquid with a gas in a relationship between vertically stacked trays in a tower. The apertures in a given tray are provided for the passage of gas in a manner less hampered by liquid coming from a discharge means of the next upper tray. This is provided by perforated housings secured to the tray deck beneath the downcomers for breaking up the descending liquid flow. Such advances in tray designs improve efficiency within the confines of prior art structures. Likewise, U.S. Pat. No. 4,543,219 assigned to Nippon Kayaku Kabushiki Kaisha of Tokyo, Japan teaches a baffle-tray tower. The operational parameters of high gas-liquid contact efficiency and the need for low pressure loss are set forth. Such references are useful in illustrating the need for high efficiency lighter fluid/heavier fluid contact in tray process towers. U.S. Pat. No. 4,504,426 issued to Karl T. Chuang et. al. and assigned to Atomic Energy of Canada Limited is yet another example of gas-liquid contacting apparatus.
Several prior patents have specifically addressed the tray design and the apertures in the active tray deck area itself. For example, U.S. Pat. No. 3,282,576 to Bruckert et al. discloses increasing tray activity by forming sloped walls at an inlet region of the tray and placing perforations on the sloped walls. By way of further example, U.S. Pat. No. 2,787,453, a 1957 patent, and U.S. Pat. No. 2,853,281, a 1958 patent, disclose directional tab-style fractionating trays that promote tray activity. Furthermore, U.S. Pat. No. 3,146,280 is a 1964 patent teaching a directional float valve. The gas is induced to discharge from the inclined valve in a predefined direction depending on the orientation of the valve in the tray deck. In addition, U.S. Pat. No. 5,098,615 to Resetarits discloses raised, perforated domes and raised, perforated channels to initiate froth and to direct fluids for improved contact.
Referring now to FIGS. 1A and 1B, a fractionation tray generally includes two or more tray sections 2 and 4 which overlap to form a joint region 5. As illustrated in FIG. 1A, many conventional methods contemplate overlapping the tray sections 2 and 4 and securing the tray sections 2 and 4 with a fastener 6 such as a bolt 6. As illustrated in FIG. 1B, some conventional methods contemplate tray sections 2 and 4 that are operable to interlock and be secured to each other without the need for fasteners. In either case, the joint region 5 is generally inactive.
Several prior patents have also specifically addressed the tray design relative to traditionally inactive areas of the tray. As illustrated in FIG. 1C, trays generally include two or more tray sections (2 and 4) that are traditionally assembled using a clamping means such as a bolt 6. For example, U.S. Pat. No. 2,582,826 to Glitsch, U.S. Pat. No. 2,903,251 to Thrift, U.S. Pat. No. 3,039,751 to Versluis, and U.S. Pat. No. 4,174,363 to Bruckert each disclose various applications of bolts in assembling trays. There have been a number of variations on the utilization of bolts in the assembly of trays. For example, U.S. Pat. No. 4,133,852 to DiNicolantonio et al. discloses welding U-shaped hinges to the trays while being bolted to a major beam. The area of overlap between tray sections, referred to herein as a joint region, is traditionally completely inactive.
More recently, as illustrated in FIG. 1D, U.S. Pat. No. 5,468,425 to Nutter discloses placing a vapor opening 7 in a joint region 5 between the two trays 2 and 4. Other improvements relative to the joint region have also been attempted. As shown in FIG. 1E, U.S. Pat. No. 6,068,244 and U.S. Pat. No. 6,422,539, both to Burton et al., teach forming trays through use of interlocking tray panels 1 and 3 and, moreover, placing a movable valve 8 in the joint region 5. As shown in FIG. 1F, U.S. Pat. No. 6,592,106 to Eaton teaches incorporating a locking mechanism 9 into the joint region 5 between the trays 2 and 4. The above-referenced patents and statements with regard to the related art are set forth for purposes of understanding the intricacies of the design considerations in contract-tray assembly and method configurations. It would be an advantage to provide a method of and apparatus for enhanced fluid flow manifesting increased efficiency through additional methodologies for activating a joint region between two or more tray sections.
Various embodiments are described herein by way of example as being applied to liquid-vapor fractionation processes. However, one skilled in the art will recognize that the same embodiments disclosed herein could also be applied to liquid-liquid extraction processes.